The present invention relates to improvements in a saw mill of the type disclosed in prior U.S. Pat. No. 4,287,798, issued Sept. 8, 1981 to Cooper et al. This class of saw mill is adapted to produce square cross section timber used for various purposes, including the production of railroad ties. A rough log must be arranged in an optimum cutting position taking into account natural irregularities by a log elevating and turning mechanism which can be called a log orientation mechanism.
One of the principal objects of this invention is to improve on the log orientation mechanism in the prior referenced patent, particularly in terms of a more positive means to turn the log on its longitudinal axis while engaging it in very narrow areas only so as to avoid contact to the greatest possible extent with nodules, limb stubs and other natural irregularities. In the referenced prior patent, the log undergoing orientation is engaged throughout its entire length so that contact with existing irregularities cannot be avoided. This, in turn, results in a less efficient and less precise optimum orientation of the log preparatory to cutting the log.
After optimum positioning of the log is achieved, the log must be dogged between its ends in preparation for a first pass through a pair of spaced rotating saw blades to remove a first pair of slabs from opposite sides of the log. Following retraction of the log transport dollies having the dogging means thereon, the log must be indexed ninety degrees in preparation for a second and final pass through the saw blades, where two more slabs are cut from the log to produce the desired square cross section timber for diverse usage.
A second principal object of this invention is to improve significantly on the dogging and indexing mechanism of the mill compared to the corresponding mechanism in the referenced prior patent. The improvement here is in two areas. First, the indexing mechanism in the present invention is not subject to any build up of rotational play as due to drive chain wear, and is very precise. Secondly, the dogged log is stabilized to a much greater degree before and after indexing and during its passage through the saw blades.
While the above are the principal improvement features over the prior art which the invention seeks to provide, other features and advantages will be recognized by those skilled in the art during the course of the following description. One such advantage of the invention over the prior referenced patent is the elimination of the need for frequent adjustment of the drive chain in the log indexing mechanism in the prior patent, such chain developing play during the usage of the mill. In the present invention, this problem is completely eliminated in the improved precision indexing and stabilizing mechanism.